Long-lost lake may have helped humans out of Africa

A GIANT, long-vanished lake along the White Nile may have been a vital way station for early humans leaving Africa. The 45,000-square-kilometre lake would be one of the world's largest lakes if it existed today, and it was in the right place at the right time for at least one of two key migrations. One took people to what is now Israel 100,000 years ago, and another peopled Eurasia 70,000 years ago.

Geologists had seen traces of an ancient lake in the arid region south of Khartoum in Sudan, but did not know when it dried up. So Martin Williams of the University of Adelaide in Australia and Tim Barrows of the University of Exeter, UK, collected samples from former lake-shore deposits, and dated them to about 109,000 years ago. They traced the lost lake along 650 kilometres of the White Nile, one of two main tributaries to the Nile. At points, the lake was almost 80 kilometres wide (Geology, doi.org/q2k).

Its peak extent came in a warm period before the last ice age. Barrows says it did not stay this large for long – the deposits formed in a few thousand years. His dating methods reveal how long it has been since the deposits were exposed, and so when the lake began to shrink.

This was a key time for humans, who appear in the fossil record in Ethiopia 200,000 years ago. By 100,000 years ago they reached the eastern Mediterranean.

But DNA shows that the ancestors of modern Eurasians left Africa later, about 71,000 years ago, says Stephen Oppenheimer of the University of Oxford. He thinks this later migration crossed the mouth of the Red Sea, when the ice age had lowered sea levels by 100 metres. "A big lake like this would have been a great place to live," he says. "It would have supported a large population, probably fishing and hunting game."

The lake was shallow and its size would have varied with the seasons. But that wouldn't have stopped people using it. "Even in arid times, these lake margins would have retained some stability," says Laura Basell of Queen's University Belfast, UK.

So far there is no way to confirm that humans lived in the area, because the current conflict in the region means it is too dangerous to return for further excavations. Nevertheless, anthropologists think it was inhabited.

However, as climate changed and the monsoon rains dwindled, the lake shrank. Its disappearance would have been a disaster for people in the area, forcing them to move elsewhere, says Ofer Bar-Yosef of Harvard University.

Migrants could have followed the Nile to the Mediterranean, and then east to Israel. So the lake's disappearance may explain the first migration out of Africa.

The lake may also have helped the later migration that peopled Eurasia, but this is less clear. It depends when it finally vanished. Barrows's analysis only shows when the lake began shrinking.

If the lake endured 70,000 years ago, it may have launched the second migration. Barrows, however, is sceptical. He says the lake "would have been long gone by 70,000 years ago".

This article appeared in print under the headline "Lost lake was a pit stop on our migration out of Africa"

Correction:When this article was first published on 22 January 2014, some instances of Tim Barrows's name were spelled incorrectly. These have now been corrected.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.